1. Field of the Invention
This invention relates to a process for the accelerating of cure rate in molding compositions comprising an unsaturated polyester resin and unsaturated monomer and it relates to promoter compositions for effecting such acceleration.
2. Description of the Prior Art
U.S. Pat. No. 4,048,086 discloses an accelerator composition which is particularly adapted for extending the shelf life of a polyester resin thickened with a calcium or magnesium oxide or hydroxide. The accelerator provided for fast cure while maintaining extended shelf life in its uncatalyzed state. The promoter consists of a cobaltic salt, e.g. cobaltic acetyl acetonate and a chemical thickener, i.e. magnesium or calcium oxide or hydroxide.
U.S. Pat. No. 3,449,276 discloses a triple accelerator system for promoting the cure of free radical catalyzed unsaturated polyester resins, the accelerator consisting of cobalt salt, a salt of an alkaline earth metal and a copper salt. The catalysts are particularly effective for accelerating free radical catalyzed polymerizable unsaturated polyester resins at low temperatures (e.g. 75.degree. F.).
Japanese Pat. No. 51-37197 discloses an accelerator system consisting of a copper halide, 2,2' bypyridine, an aromatic amine, and a cobalt salt. The examples show that these accelerators, typically containing a cobalt naphthenate salt, copper chloride, bipyridine, and dimethyl- or diethylaniline give fast cure times when the polyester resin was catalyzed with the methylethyl ketone peroxide, the curing being effected at room temperature (25.degree. C.)
The industry standard for promoting the cure of molding compounds at low temperatures has been a mixture of a cobalt salt and an aromatic amine, e.g. dimethylaniline. Although these accelerator compositions are extremely effective for providing fast cure times, the prepromoted polyester resin in its uncatalyzed state has an extremely short shelf life, e.g. 1 to 3 days.